Python嵌套类定义报错修复求助：LeetCode #1032开发问题

问题重现 #

我在开发LeetCode #1032题目时遇到嵌套类相关的错误，代码如下：

from collections import deque

class StreamChecker:

    def __init__(self, words):
        self.RPT = StreamChecker.ReversePrefixTree( StreamChecker.ReversePrefixTreeNode )
        
    def query(self, letter):
        ...
    
    class ReversePrefixTreeNode:
        def __init__( self ):
            self.char_dict = {}      # Key is char from word, value is successor node
            self.words = []          # All words that complete at this node
        def successor( self, char ):
            return self.char_dict.get( char, None )
        def getWords( self ):
            return self.words
        def __str__( self ):  return f"[ RPTNode: char_dict = { self.char_dict }, words = { self.words } ]"

    class ReversePrefixTree:
        def __init__( self, root ):
            self.root = root
        def insert( self, word ):
            node = self.root
            for char in reversed( word ):
                if char in node.char_dict:
                    node = node.char_dict[ char ]
                else:
                    next_node = ReversePrefixTreeNode()
                    node.char_dict[ char ] = next_node
                    node = next_node
            node.words.append( word )

def tester():    
    obj = StreamChecker( [ "here", "are", "some", "words" ] )
    print( "obj", obj, "obj.RPT", obj.RPT )
    print( "obj.RPT.root", obj.RPT.root.getWords() )    # 问题行
    
tester()

运行后报错：

obj <__main__.StreamChecker object at 0x00000213C5FB1710> obj.RPT <__main__.StreamChecker.ReversePrefixTree object at 0x00000213C5FB3E50>
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[22], line 41
     38     print( "obj", obj, "obj.RPT", obj.RPT )
     39     print( "obj.RPT.root", obj.RPT.root.getWords() )
---> 41 tester()

Cell In[22], line 39, in tester()
     37 obj = StreamChecker( [ "here", "are", "some", "words" ] )
     38 print( "obj", obj, "obj.RPT", obj.RPT )
---> 39 print( "obj.RPT.root", obj.RPT.root.getWords() )

TypeError: StreamChecker.ReversePrefixTreeNode.getWords() missing 1 required positional argument: 'self'

明明通过对象路径调用方法，却提示缺少self参数，这是为什么？

错误原因 #

核心问题是你把ReversePrefixTreeNode类本身传给了ReversePrefixTree，而不是创建该类的实例：

• 在StreamChecker.__init__中，你传入的是StreamChecker.ReversePrefixTreeNode（类对象），而非StreamChecker.ReversePrefixTreeNode()（类的实例）。
• 因此ReversePrefixTree的self.root存储的是类，不是实例。当你调用obj.RPT.root.getWords()时，本质是调用类的未绑定方法，Python不会自动传入self参数，所以报错。

另外还有一个隐藏问题：在ReversePrefixTree.insert方法中，直接写ReversePrefixTreeNode()会因为嵌套类作用域问题找不到该类，需要明确引用外层类的嵌套类。

修复方案 #

1. 初始化时传入节点实例：在StreamChecker.__init__中，将StreamChecker.ReversePrefixTreeNode改为StreamChecker.ReversePrefixTreeNode()，创建实例传给ReversePrefixTree。
2. 正确引用嵌套类创建节点：在ReversePrefixTree.insert中，将next_node = ReversePrefixTreeNode()改为next_node = StreamChecker.ReversePrefixTreeNode()。

完整修正代码 #

from collections import deque

class StreamChecker:

    def __init__(self, words):
        # 传入ReversePrefixTreeNode的实例，而不是类本身
        self.RPT = StreamChecker.ReversePrefixTree(StreamChecker.ReversePrefixTreeNode())
        # 插入所有单词到前缀树中
        for word in words:
            self.RPT.insert(word)
        
    def query(self, letter):
        # 补充你的query逻辑
        pass
    
    class ReversePrefixTreeNode:
        def __init__(self):
            self.char_dict = {}      # Key is char from word, value is successor node
            self.words = []          # All words that complete at this node
        def successor(self, char):
            return self.char_dict.get(char, None)
        def getWords(self):
            return self.words
        def __str__(self):  
            return f"[ RPTNode: char_dict = {self.char_dict}, words = {self.words} ]"

    class ReversePrefixTree:
        def __init__(self, root):
            self.root = root
        def insert(self, word):
            node = self.root
            for char in reversed(word):
                if char in node.char_dict:
                    node = node.char_dict[char]
                else:
                    # 明确引用外层类的嵌套类创建实例
                    next_node = StreamChecker.ReversePrefixTreeNode()
                    node.char_dict[char] = next_node
                    node = next_node
            node.words.append(word)

def tester():    
    obj = StreamChecker(["here", "are", "some", "words"])
    print("obj", obj, "obj.RPT", obj.RPT)
    print("obj.RPT.root words:", obj.RPT.root.getWords())
    
tester()

内容的提问来源于stack exchange，提问作者Mark Lavin